This invention relates to the manufacture of an oval diaphragm and its use in an essentially circular housing of a brake booster.
U.S. Pat. Nos. 3,083,698, 3,158,930 and 6,390,567 are typical of brake boosters manufactured through a well known methods. In such manufacture an end surface on a first shell is crimped or deformed by cutting or shearing tabs that engage a surface on a second shell to join a first shell with a second shell and define a unitary structure. In joining the first shell to the second shell, a first bead of a diaphragm associated with a movable wall is retained between the first shell and the second shell while a second bead is connected to the movable wall to separate the interior into a front chamber from a rear chamber.
The diaphragm in such brake boosters is normally constructed in a mold through an injection molding process. The mold will have a diameter wherein material flows from a center port toward the radius such that a uniform cross section is produced without a seam or mold line. The first bead and second bead are located in the mold in accordance with a desired diameter size for a brake booster with the first bead being at an outer peripheral position and the second bead being at an radius from the center of the mold. After the molding, the resulting diaphragm is trimmed to the desired size such that the first and second beads are now respectively located on inner and outer peripheral surfaces. Unfortunately, such molding process may result in substantial scrap depending on the position of the second which can be located on a shoulder of a hub of the movable wall or on in a groove on a backing plate for the movable wall. In any case, radius from the center of the molded disc to the second bead represents scrap and a waste of material.
A primary object of the present invention is to manufacture a diaphragm for a brake booster wherein an inner bead has an initial oval shape that is stretched into a circular shape for insertion into an annular groove of a movable wall to isolate a front chamber from a rear chamber.
According to this invention, a brake booster has a first shell joined to a second shell by deforming a first peripheral surface on the first shell with respect to a second peripheral surface on the second shell to define a housing. A diaphragm has a first bead located between the first and second peripheral surfaces and a second bead secured to a movable wall such that the interior of the housing is divided into a front chamber and a rear chamber that are sealed with respect to the surrounding environment. The movable wall carries a valve arrangement that initially responds to a brake input to interrupt communication between the front chamber and the rear chamber and thereafter open communication between the rear chamber and the surrounding environment to create a pressure differential across the movable wall. The pressure differential acts on the movable wall to develop an output force for effecting a brake application. The movable wall is characterized by a disc having an annular groove located adjacent a peripheral outer surface while the diaphragm is characterized by a cylindrical body with a first section that transitions into a first bead on a first end and a second section that transitions into a second bead on a second end. The first bead and the second bead each have an initial oval shape that is stretched into a circular shape for respective retention between the first and second peripheral surfaces annular groove to define a connection between the movable wall and the first and second peripheral surfaces in sealing the front chamber from the rear chamber.
An advantage of this invention resides in a brake booster having a diaphragm wherein at least an inner bead having an oval shape is stretched into a circular shape for retention in an annular groove to define a sealed joint between the diaphragm and a movable wall.
A still further advantage of this invention resides in a method of manufacture of a diaphragm with a cylindrical central section that transitions into an oval section containing a bead such that the diaphragm is trimmed adjacent the bead and thereafter stretched into a circular shape for retention in a annular groove in a movable wall.
A still further advantage of the present invention resides in a method of manufacturing a diaphragm wherein scrap is reduced by defining an inner bead with an oval shape that is stretched into a circular shape for retention in a groove in a movable wall.